The present invention relates generally to equipment utilized in subterranean wells and, in an embodiment described herein, more particularly provides a compact retrievable packer.
Packers are typically made up of a large number of components. Each of these components must be designed, tested, manufactured, inspected, inventoried, assembled with the other components, etc., in order to produce a certain type of packer for use in a particular size of casing or other tubular member in which the packer is to be set. As used herein, the term "set" is used to indicate that an apparatus has been operated to sealingly engage and grippingly engage a tubular member, or only sealingly engage or grippingly engage the tubular member if it is designed to perform one but not the other of those functions.
Unfortunately, due to the limitations of current packer designs, a packer is typically usable in only one or a few different weight ranges of a particular casing size. This is caused in part by the fact that a predetermined radial clearance exists between the outside diameter of the packer and the inside diameter of the particular casing size and weight. Thus, components designed for use in a packer in a particular size and weight of casing may not be usable in another packer in a different size or weight of casing and, therefore, these components must be designed, tested, manufactured, etc. for each packer and each size and weight range of casing.
Accordingly, it would be highly advantageous to provide a packer which includes a small number of components, and which is usable in a wide range of casing sizes and weights. This would greatly reduce the time and expense required for designing components for the packer, testing the packer, manufacturing, inspecting, shipping and warehousing the components, assembling the packer, etc. However, in order to achieve the objective of usability in a wide range of casing sizes and weights, the problem of variable radial clearance between the packer and casing inner diameter must be solved.
In the past, packers have typically been designed so that the radial clearance between the packer and a particular casing inner diameter is as small as possible, while still permitting the packer to be displaced through the casing. Unfortunately, due to tolerances in packer and casing manufacture, the presence of scale, corrosion, various contaminants, such as salt pills, adhered to the casing inner diameter, etc., the radial clearance must be comparatively large. This problem is compounded by the fact that the radial clearance is also an extrusion gap for seal elements carried on the packer, which must be radially outwardly extended to seal against the casing inner diameter.
When the seal elements are outwardly extended, they bridge the radial clearance and prevent fluid flow between the packer and the casing. Since fluid pressure applied to one side of the seal elements will cause them to extrude into the gap between the packer and casing on the other side, the radial clearance is also an extrusion gap. Failure of the seal elements to seal against fluid pressure is often caused by excessive extrusion of the seal elements into the extrusion gap.
In order to prevent such failure of the seal elements, various attempts have been made to minimize or eliminate the extrusion gap, or to increase resistance of the seal elements to such extrusion. For example, backup rings may be installed straddling the seal elements in an attempt to close up the extrusion gap, but this increases the number of packer components and does not increase the packer's usability in other casing sizes and weights. As another example, the seal elements may be made of exotic extrusion-resistant materials or provided with "garter springs" to increase extrusion resistance, but these increase the cost of the seal elements and still do not increase the packer's usability in other casing sizes and weights.
It would, therefore, also be highly advantageous to provide a packer which has the capability of closing off the extrusion gap, while still permitting sufficient radial clearance between the packer and a wide variety of casing sizes and weights during run-in and retrieval of the packer. It would be even more advantageous to provide such a packer which did not require additional components for closing off the extrusion gap, and which did not require the seal elements to be made of expensive materials or to include devices such as "garter springs" therein.
In general, the seal elements on a conventional packer are radially outwardly extended by axially compressing the seal elements between annular gauge rings or element retainers mounted on the packer. One or both of the gauge rings or element retainers is axially displaceable relative to the other one of them, in order to squeeze the seal elements between them. Achieving such displacement of the gauge rings or element retainers requires complex mechanisms and, since there are limitations on the amount of squeeze and radial extension available for a given set of seal elements, these vary depending upon the size and weight of the casing for which the packer has been designed.
Thus, it would also be advantageous to provide a packer which does not require complex mechanisms for axially compressing seal elements, and which does not require axial compression of its seal elements in order to radially outwardly extend the seal elements. In this manner, the packer would be usable in a wider range of casing sizes and weights, and the packer would be less expensive to design, manufacture, inventory, assemble, etc.
Since there are limitations on the amount of radial extension typically available from a given set of seal elements on a given packer, the packer is frequently designed with the seal elements having an outer diameter only slightly smaller than the inner diameter of the casing in which the packer is designed to be set. This situation may result in the seal elements being abraded, cut, eroded, or otherwise damaged while the packer is being conveyed into, and positioned within, the casing, although it is common practice for a set of gauge rings on the packer to have a slightly larger diameter than the seal elements.
It would, therefore, be advantageous to provide a packer which permits the seal element to spaced away from the casing inner diameter by a comparatively large clearance while conveying and positioning the packer within the casing, and yet the packer still having the capability to radially outwardly extend the seal element into sealing engagement with the casing and the capability to eliminate the extrusion gap between the packer and the casing. Such capabilities would be even more advantageous in applications in which the packer must pass through restricted diameters before being set in the casing, such as in "slim hole" applications in which the packer must pass through a relatively small diameter tubing string before being set in a larger diameter casing.
Conventional tools, such as packers, tubing hangers, etc., are commonly provided with components collectively referred to as "slips", which act to anchor the tools within casing or other tubular members. The ability of such a tool to resist forces applied thereto depends in large part upon the amount and distribution of gripping contact of the slips with the tubular member inner diameter. In addition, complex mechanisms are typically required to radially outwardly extend the slips, and to time the extension of the slips where it is desired to achieve a particular sequence of setting the tool. For example, it may be desired to have a lower set of slips grip the inner diameter, then for the seal elements to seal against the inner diameter, and then for an upper set of slips to grip the inner diameter.
Therefore, it would be advantageous to provide a tool which includes slips that uniformly grip the tubular member inner diameter, which have a large amount of gripping contact with the inner diameter, and which do not require complex mechanisms for achieving such gripping engagement. Furthermore, it would be advantageous to provide the tool having the capability of conveniently achieving a particular sequence of engagement with the inner diameter, without requiring additional components, complex mechanisms, etc.
Additionally, it would be advantageous to provide a packer which is conveniently retrievable, without requiring complex mechanisms for such retrieval. Furthermore, if conventional attempts to retrieve the packer are unsuccessful, it would be advantageous to be able to retrieve a significant portion of the packer before the packer is milled, thereby reducing the time required to mill the packer. Still further, if milling of the packer is necessary, it would be advantageous for a mechanism which releases the packer from engagement with the casing to be positioned near the top of the packer, so that the packer will be released most expeditiously.
It would also be advantageous to provide a packer which is of modular design. In this manner, greater or fewer seal elements, slips, etc. may be installed on the packer for use in different applications, such as low pressure or high pressure applications. This would reduce the amount of inventory necessary to provide for such different applications, while increasing the versatility of the packer.
From the foregoing, it can be seen that it would be quite desirable to provide a packer which has the above advantages, but which is still capable of withstanding relatively high pressures and forces applied thereto. Of course, these advantages would also be desirable in other tools, such as tubing hangers, etc. It is accordingly an object of the present invention to provide such a packer and such other tools.